Alpha blending has strange artifacts as show on the pipes and metal objects in this illustration:

It's a common problem of Blend type of alpha transparancy, it's can't be fixed. So we recomended using of blend type of the alpha only for simple geometry like planes and not closed on itself geometry.

Of all the alpha blending options, only the "Add" option seems to create smooth blends. The same transparency option seems to work on my other model:

For tubes, spheres and all complex geometry better to use alpha add, so you'r doing it right.